Strange Creatures in Foreign Places

Spinybacked Orbweaver spider.

These spiders are about 6mm or 1/4" across the spines, not terribly big. Definitely showing its distant relationship to crabs. It's hanging head down, in case you were wondering. I've seen them around Georgia for years, and have always wanted a decent picture of one. That proved challenging, but a good look at my camera's manual allowed me to finally figure out how to do manual focus (as the auto-focus won't work on such a small object that close up).

Does anyone know the name of these? Colloquial or Scientific, I don't care.

Update: Thanks to Brianne, this has been identified as a Spinybacked Orbweaver (Gasteracantha cancriformis).